1. Field of the Invention
This invention relates to fuel burners having high flame stability and to such fuel burners for heating the intake air of an internal combustion engine.
2. Discussion of the Prior Art
A fuel burner design has long been desired which satisfies the sometimes conflicting goals of low manufacturing and maintenance cost and of high flame stability and insensitivity to ambient air currents. These goals are particularly important to manufactures and users of internal combustion engines of the compression ignition type (diesel) since fuel burners are normally provided in the intake manifold of such engines to promote easier starting and to reduce exhaust smoke and other noxious emissions. A stable flame is particularly critical to the proper operation of burners used to preheat air within the intake manifold of an internal combustion engine since insufficient combustion will cause difficult starting and noxious exhaust emission and excessive combustion will deplete the available oxygen supply within the intake manifold thereby possibly preventing engine start up altogether.
A variety of burner designs have been proposed for use within an engine intake manifold such as illustrated in U.S. Pat. No. 3,687,122, assigned to the assignee of this invention. Each of the disclosed designs includes a fuel nozzle supplied with both fuel and air and a shroud for containing and directing the burner flame. While reasonably successful in achieving flame stability the various shroud designs disclosed in U.S. Pat. No. 3,687,122 are not always effective to prevent flame blow out and to insure sufficient heat generation without excessive consumption of fuel or oxygen within the intake manifold. This ineffectiveness derives in part from the requirement that an additional amount of air be supplied to the burner flame beyond the air supplied to the fuel nozzle in order to insure complete combustion of the burner fuel. Since this requirement is normally met by supplying air from the intake manifold to the burner flame through an opening in the shroud near the flame base, fluctuation in pressure and changing air flow within the intake manifold can have adverse effects on flame stability. Even where the flame shroud takes the form of a cup which completely surrounds and separates the flame base from the intake manifold, erratic fuel combustion can occur as a result of turbulent air flow into and out of the open end of the cup shaped shroud. Moreover, cup shaped shrouds must still be provided with an auxiliary flow of air near the base of the burner flame to insure complete combustion. This additional air is normally supplied through a conduit connected with an outside source of air such as illustrated in U.S. Pat. No. 3,977,377, also assigned to the same assignee as this invention. Such an auxiliary supply of air can add substantial cost to an intake preheater device while still not achieving optimum results.
One attempt to solve this dilemma is disclosed in U.S. Pat. No. 4,044,740 wherein a burner assembly having inner and outer annular casings are illustrated for disposition within an engine inlet manifold. While more efficient combustion and greater flame stability may be achieved with this burner design as compared with prior art designs, the complicated arrangement of inner and outer casings adds to manufacturing costs over previous designs and the obstructed exit passage for the combustion gases can lead to carbon deposits and excessive maintenance costs.
Another attempt to provide an efficient and yet highly versatile intake air burner assembly is illustrated in U.S. Pat. No. 4,027,642 wherein a fuel nozzle is mounted near the base of a cup shaped shroud which opens into the intake manifold of an engine. Auxiliary air is provided to the flame area through an opening adjacent one side of the combustion gas outlet of the cup shaped shroud apparently resulting in some recirculation of combustion gases within the cup shaped shroud. However, the recirculation path is illustrated as being nonsymmetric and thus subject to irregular behavior and flame instability.
Outside of the intake air heater art, it has been disclosed for example in U.S. Pat. No. 2,033,838, to provide a fuel burner with a shroud including a cylindrical body portion for surrounding the liquid fuel nozzle wherein the shroud includes a combustion gas outlet opening defined by an inturned lip. This patent further discloses a fan designed to force air through the shroud and out the aperture defined by the inturned lip thereby adding to the cost and complexity of the burner. In short, no prior art fuel burner has taught a simple yet effective way of achieving sufficient flame stability to meet the stringent requirements of an effective intake air preheater device.